The present invention generally relates to a turbocharged automobile engine having an exhaust purifier on the exhaust system thereof and, more particularly, to a combination of the turbocharged engine with means for controlling the flow of exhaust gases through the exhaust driven turbine to accelerate warm-up of the exhaust purifying unit.
A turbocharged automobile engine having an exhaust purifying unit, for example, a catalytic converter or a thermal reactor (exhaust afterburner) is well known. The turbocharger comprises a blower or compressor, disposed on the intake system for the introduction of intake gases towards the engine, and an exhaust driven turbine disposed on the exhaust system for the discharge of exhaust gases towards the atmosphere. The compressor and the turbine are drivingly linked together to allow the compressor to be driven by the turbine then driven by the flow of the exhaust gases therethrough. The purpose of use of the turbocharger, and the advantage derived therefrom, are well known in the art.
When it comes to the use of the turbocharger in combination with the exhaust purifying unit, for example, the catalytic converter, which generally requires to be heated to its operating temperature in order for it to exhibit an acceptable performance, the presence of the exhaust driven turbine on the exhaust system upstream of the catalytic converter with respect to the direction of flow of the exhaust gases towards the atmosphere brings about a problem associated with the warm-up of the catalytic converter because in many cases the catalytic converter relies on the heat of the exhaust gases. More specifically, all of the structural elements of the turbine, as well as all of the pipings leading to and from the turbine, which are exposed to the flow of the exhaust gases, necessarily absorb heat from the exhaust gases and, therefore, during a particular engine operating condition, for example, a cold start of the engine, it often happens that the catalytic converter cannot be quickly warmed up to the operating temperature, allowing the emission of obnoxious exhaust compounds for a substantial time before it is subsequently heated to the operating temperature.
According to U.S. Pat. No. 4,244,187, patented Jan. 13, 1981, there is disclosed a solution to the above discussed problem. According to it, in addition to the well known bypass passage connecting the turbine inlet with the turbine outlet and having a waste gate disposed therein, another bypass passage is provided which may be termed as a shortcut passage as it connects the engine exhaust port or ports with the catalytic converter in a minimized distance. This shortcut passage provides a fluid circuit extending in parallel to the bypass passage having the waste gate, the inlet of which is provided with a switching valve for selectively directing the flow of exhaust gates towards the catalytic converter directly through the shortcut passage and through the turbocharger turbine. For controlling the switching valve, this U.S. patent makes use of an actuating and control means operable to cause the switching valve to direct the flow of exhaust gases towards the catalytic converter through the shortcut passage during the warm-up period to quickly heat the catalytic converter and also operable to cause the switching valve to direct it towards the catalytic converter through the turbine for normal power recovery after the warm-up period. The actuating and control means includes an electromagnetic valve assembly adapted to be electrically energized in response to the increase of temperature of at least one of the engine cooling fluid, the exhaust piping and the catalytic converter, and a spring-biased diaphragm valve having a diaphragm operatively coupled with the switching valve and having spring and non-spring chambers defined therein on respective sides of the diaphragm. The electromagnetic valve assembly is so designed that, when and so long as it is not energized on account of the temperature of the catalytic converter having not yet reached a predetermined value, the valve assembly can direct the vacuum, drawn at a portion of the intake system upstream of the compressor, to the spring chamber of the diaphragm valve, while the non-spring chamber is vented to the atmosphere, causing a pressure differential that will overcome the spring force acting on the diaphragm and move the switching valve so as to block the flow of exhaust gases through the turbine.
Aside from the problem associated with the warm-up of the exhaust purifying unit, attempts have been made to improve the turbocharger with a view to further increasing the maximum available power output of the automobile engine even at a low engine speed. By way of example, the Japanese Laid-open Utility Model Application No. 56-161139, published Dec. 1, 1981, discloses the turbine inlet passage so divided and so partitioned only at a portion adjacent the turbine inlet as to provide a main passage section and a controllable passage section, which controllable passage section is adapted to be choked either when the engine speed is low or when the load on the engine is high and to be opened either when the engine speed is high or the load on the engine is low.
Japanese Laid-open Patent Publication No. 58-176417, published Oct. 15, 1983, discloses the use of at least one pivotally supported vane member so disposed in the vicinity of the turbine inlet as to adjust the effective cross-section of the turbine inlet nozzle according to the engine operating condition represented by the engine speed and/or the load on the engine. Specifically, at a high engine speed, the vane member is in position to increase the nozzle cross-section to its maximum value, but at a low engine speed, the vane member is in position to reduce the nozzle cross-section to allow the exhaust gases to flow at a high velocity through the turbine thereby driving the latter at a high speed for the quick boosting of the engine output power. A similar example, but wherein the vane member can assume one of the two opposite, "fully open" and "reduced" positions according to a particular engine operating condition, is also disclosed in Japanese Laid-open Patent Publication No. 60-19918.
While all of the above mentioned Japanese publications are silent as to the use of the exhaust purifying unit in the environments of the turbocharged engine, it has been found that even the throttling of the flow of the exhaust gases entering the turbocharger turbine constitutes an additional cause of the reduced exhaust temperature. More specifically, as the exhaust gas flow is throttled by the vane member, the turbine can be driven at an increased speed. However, the higher the flow of the exhaust gases entering the turbine, the greater the amount of heat energy of the turbine, and the temperature drop of the exhaust gases is correspondingly accelerated.
In view of the fact that the catalytic converter can work satisfactorily when and after heated to the operating temperature as is well known to those skilled in the art, the exhaust temperature drop which may occur for any reason before the exhaust gases enter the catalytic converter is desired to be minimized. Particularly during, and possibly for a moment subsequent to, the cold start of the engine at which time not only is the engine speed generally low, but the engine is cool with the exhaust temperature still low, the minimization of the exhaust temperature drop is very important. The throttling of the exhaust gas flow according to any one of the above mentioned Japanese publications may further lower the exhaust temperature which might have been lowered in contact with wall components forming the exhaust system of the engine, and therefore, the catalytic converter can not be quickly heated to the operating temperature.